Rock Slope Protection Utilizing a New WSDOT Designed Hybrid Drapery System in Conjunction with Traditional Stabilization Techniques

The US2 West of Leavenworth Slope Stabilization project was located on the eastern slope of the Cascade Mountains within a deeply incised valley named Tumwater Canyon. This project mitigated rockfall events along approximately 2500 feet of highway. Rockfall sources included bouldery colluvium that discontinuously mantled the bedrock on over-steepened slopes, and structurally controlled rock slope failures. To develop the mitigation designs, planar and wedge type failures, snow loading on cable net installations, rockfall bounce heights, and kinetic energies were evaluated. The mitigation work included rock slope scaling, debris removal, untensioned rock dowels, post-tensioned rock bolts, horizontal drains, shotcrete facing, cable net slope protection, and WSDOT’s newly designed hybrid drapery system. This new design addresses rockfall with kinetic energies of up to 100 ft-tons and bounce heights of up to 18 ft. Lessons learned from this project included the need for a more defined procedure to locate posts and to determine post foundation types, the need for a new micropile post foundation type for posts constructed on steep colluvial slopes, the need for instructions to address alternative maximum post spacing, the need for specified minimum tension values or maximum sag on the post-support cables, the need for improved procedures for constructing grout pads and how to place post-support cable anchors, and needed plan revisions better defining termination and the lay of the cable nets on the slope. Post foundations will also now be bid as a separate item rather than included within a single bid item for the total installed square footage of cable nets.


  • English

Media Info

  • Media Type: Digital/other
  • Features: Figures; Photos; References;
  • Pagination: pp 38-52
  • Monograph Title: Proceedings of the 63rd Annual Highway Geology Symposium (HGS 2012)

Subject/Index Terms

Filing Info

  • Accession Number: 01661531
  • Record Type: Publication
  • Files: TRIS
  • Created Date: Feb 8 2018 4:10PM